1. Field of the Invention
This invention relates to photoconductive coating compositions and, more particularly, to dye-sensitized zinc oxide/resin binder compositions that have good thermal stability.
2. Description of the Prior Art
Electrophotography is an imaging process that typically involves placing a uniform charge on the surface of a photoconductor in the dark; imagewise exposing the charged photoconductor, thereby discharging it in the exposed areas; and applying to the surface a toner that is preferentially drawn to (or repelled from) the charged areas. To form a lasting image, the toner may then be fused on the surface or, alternatively, transferred to and fused on a receptor. Optionally, as is described in U.S. Pat. Nos. 2,952,536 and 2,957,765, treatment with a conversion solution containing, for example, ferrocyanide ions, can render toned and untoned areas oleophilic and hydrophilic, respectively, to provide a lithographic printing plate.
Photoconductive zinc oxide, dispersed in a resin binder, and, optionally, dye-sensitized is a well known system for electrophotography (see, e.g., R. M. Schaffert, Electrophotography, Focal Press, New York, 1973). Typically, a zinc oxide/resin binder system is coated on paper, and a toned image formed on its surface is fixed directly on the coating, without need to transfer the image to a receptor.
Resin binders suitable for use with zinc oxide in photoconductive compositions and, in particular, resin binder blends (or mixtures) have been disclosed in U.S. Pat. No. 3,345,162, issued Oct. 3, 1967, to S. B. McFarlane, Jr. et al.; U.S. Pat. No. 3,347,670, issued Oct. 17, 1967 to G. R. Nelson et al.; and U.S. Pat. No. 3,615,419, issued Oct. 26, 1971, to S. Field. Styrene acrylate resins as binders for photoconductive compositions are disclosed in U.S. Pat. No. 3,540,886, issued Nov. 17, 1970, to R. E. Ansel, et al. Vinyl acetate resin binders are disclosed in U.S. Pat. No. 3,378,370, issued Apr. 16, 1968, to S. T. Brancato; U.S. Pat. No. 3,607,376, issued Sept. 21, 1971 to R. B. Blance et al.; and U.S. Pat. No. 3,745,006 issued July 10, 1973 to R. B. Blance et al.
Among the dyes that have been found to be useful for spectral sensitization of zinc oxide are cyanine dyes. Cyanine dye-sensitization has been disclosed in U.S. Pat. No. 3,619,154, issued Nov. 9, 1971, to G. A. Cavagna et al. Similar dyes as sensitizers in thermally-stable, infrared-sensitive photoconductive compositions have been disclosed in Japanese Application (kokai) No. 7,046,245, published Mar. 16, 1982.
Zinc oxide electrophotographic coatings containing cyanine sensitizers and multicomponent binders were disclosed by W. C. Park in his U.S. Pat. No. 3,682,630, issued Aug. 8, 1972, and his paper-TAPPI, 56, 101 (1973).
The use of a laser diode as an exposure source for recording on electrophotographic material was disclosed by A. Stramondo in 1980 Proceedings of Lasers in Graphics, Electronic Publishing in the 80's Conference, Vol. 1, page 1-27.